Method of making valves for internalcombustion engines



A ril 23, 1968 PRMSSE ETAL 3,378,904

METHOD OF MAKING VALVES FOR INTERNAL-COMBUSTION ENGINES Filed June 22, 1965 Gisela Prasse Harry Merkf INVENTORS.

To (5 M d m United States Patent Office Patented Apr. 23, 1968 7 Claims. c1: 29--156.7)

Our present invention relates to improvements in the production of so-called poppet valves of the mushroom or tulip types employed in internal-combustion engines and, more particularly, to sodium-filled poppet valves having a sealed cavity extending from the valve head through the stern for expediting the conduction of heat from the valve head to the stem from whence it is dissipated.

The advantages of such hollow valves are discussed in the commonly assigned copending application Ser. No. 252,497, filed Jan. 18, 1963, by Gerhard Kubera (now US. Patent No. 3,358,350 of Dec. 9, 1967), the internal cavity of such valves being filled with metallic sodium or other liquefiable metal Whose high thermal conductivity is exploited to facilitate the cooling of the portions of the head exposed to the combustion gases and exhaust gases of the cylinder. While the hollow valve described in this copending application has a head formed integrally with the stern and the present invention is applicable thereto, it has been a common practice heretofore to produce the valve from a head or crown which is welded to the stem (e.g. as described in US. Patent No. 2,407,- 561 of Sept. 10, 1946). In accordance with this common method of producing valves for internal-combustion engines, both the stem and the head are hollow-forged individually and are joined together. For the most part, this method involved the production of a stern closed at one end so that, immediately after the internal cavities of the members were filled with sodium to the desired degree, the head and stem members were joined together by welding, the valve then being subjected to a temperature of 700-800 C. in a heat treatment designed to remove stresses.

During the hollow-forging of the valve members, how ever, an oxidized layer of the metal of the body is formed along the Walls of the cavity and constitutes a barrier to heat transfer between the metallic body and the metallic sodium. This disadvantage will become all the more apparent when it is realized that the steels used in such bodies are usually refractory or contain refractory components which, when oxides are formed, impart to such layers the nature of a ceramic; refractory oxides of this type not only are difficult to dislodge by mechanical means but are substantially inert and unaffected by the annealing temperatures generally used for treatment of the valve body and are resistant to attack by metallic sodium at the customary temperatures at which the valve is used or to which it is subjected. Thus the production of sodium-filled valves for the exhaust ports of internalcombustion engines has been disadvantaged by a dichotomy between the use of sodium to increase the heat transfer between the head and the stem and the formation of oxides in the provision of a receptacle for the metallic sodium, such oxides impeding the heat transfer. Conventional sodium-filled valves have thus been subjected, to a certain extent, to distortion and deterioration resulting from an insufficient ability to rapidly transfer heat away from the head and have only limited useful lives.

It is an important object of the present invention to provide an improved method of making valves of this character whereby the useful life of the valve can be improved and thermal distortion thereof reduced.

Another object of this invention is to provide a method of making sodium-filled internal-combustion-engine valves having an increased rate of heat transfer from the head to the stem and thermal dissipation thereby.

These objects and others which will become apparent hereinafter are attained in accordance with the present invention, by a method based upon our discovery that the thermal transfer between metallic sodium within a cavity of a valve body and the valve body itself can be sharply increased by a chemical attack upon the thermal barrier; more particularly, we have found that, when a sodium-filled valve body is sealed and brought to a temperature in excess of the boiling point of sodium, an etching of the barrier layer can be effected by the sodium in such manner as to completely eliminate or permit penetration of the barrier without destroying the valve body. Heat transfer between. a wall of the cavity of the valve body and the metallic sodium is expedited and the tendency of the valve toward deterioration at elevated temperatures is reduced. In addition, the useful life of the valve is markedly improved.

The present invention is carried out preferably by heat ing the valve body, after welding it closed, to a temperature of substantially 10001050 C. for a period suflicient to result in substantial chemical action upon the oxide layer along the cavity walls.

According to another feature of this invention, the heating of the valve body to a temperature sufiicient to vaporize the sealed-in sodium is used to test the closure seam or seams for inherent weakness. It is known, for example, that welded seams frequently have the appearance of perfection but, in reality, contain inclusions or are formed with dislocations and minute cracks undetectable by visual testing methods and requiring complex equipment for the determination of defects. In accordance with this aspect of the present invention, the testing of the sealed valve member is effected by raising the temperature above the boiling point of sodium to thereby increase the pressure within the cavity and strain any imperfections in the Welding seam while concurrently etching the seam or chemically attacking same to effect a high-rate deterioration of imperfect portions. Any minute crevices in the seam are thus; rapidly widened and enable the defective blank to be detected.

Another advantage of this invention resides in the fact that the elevated temperature of 10004050 C. preferably used for the present process gives rise to a complete grain transformation in the region of the weld. It is common knowledge that the formation of a welding seam between the two interconnected members gives rise to a coarsegrain structure in the region of the weld. Such structures are prone to fatigue and stress failure and are, therefore, disadvantageous in valves for internal-combustion engines. The high-temperature treatment of the valves according to the present invention results in a grain transformation in which the coarse-grain structure is converted into a fine-grain structure of improved qu'ality.

The above and other objects, features and advantages of the present invention will become .more readily apparent from the following description, reference being made to the accompanying drawing in which the sole figure is an axial cross-sectional view through a valve stem embodying the present invention.

In the drawing we show a mushroom-type valve for an internal combustion engine whose stem 10 is hollowforged at 11 to form a cavity for metallic sodium or some other coolant of similar character.

Other cool-ants include sodium/mercury amalgarns and other low-melting metals which normally have a melting 3 point at or just below the engine-operating temperatures in the region of the exhaust valves of the engine block but a boiling point far above these operating temperatures so that the cooling material is in liquid state during engine operation although it may solidify upon termination thereof. The foot 13 of the stem is shaped to receive the valvelifting mechanism while the valve head is formed by a plate or disk 14 welded at a seam 15 to the stem 1%. As indicated earlier, the present invention is operable with crowned or mushroom-type heads 14 although so-called tulip heads may be employed. Moreover, in certain cases valves having plugs at foot 13 to close the internal cavity may also be used. After the sodium, preferably freed completely from any traces of the petroleum distillate (e.g. kerosene) in which the sodium metal is kept to prevent oxidation, is introduced into the interior of the valve body, the valve head 14 is immediately welded to the stem as described in US. Patent 2,407,561 and the entire structure subjected to heating at 10G01050 C. for a period of, say, on the order of minutes. The result ing etching of the oxide surface of the cavity has been found to increase the thermal conductivity of the valve member and thus its life on the order of several times. The heating step, moreover, has been shown by microscopic analysis to result in a transformation of the grain in the region of the weld; moreover, when the method was used in serial production, valves having defective welds, were readily detected as a result of the high pressures developed within the valve body and, apparently, the rapid chemical action at otherwise obscure crevices thereof.

Prior to introduction of the coolant metal, the interior of the valve body is scoured with an oil-solubilizing alkali to remove any traces of oleo-organic materials which may be volatile at the operating temperatures of the engine.

This precaution is taken and the sodium is introduced only after being freed from traces of its protective liquid to avoid the possibility that volatilization of organic substances within the cavity at the operating temperatures of the valve or at the heat-treatment temperature to which it is subjected will generate pressures capable of rupturing the valve body or materially weakening it.

By way of a specific example, it may be pointed out that a suitable valve body can be formed from nickelchromium steels (e.g. 18% by weight chromium, 4% by weight nickel, 3% by weight molybdenum, 0.15% by weight nitrogen, 0.20.4% by weight carbon, balance iron). The welding head can be a high-temperature steel alloy and can, for example, consist of substantially 0.12% by weight carbon, 2% maximum manganese, 1% maximum silicon, by weight chromium, 46% by weight nickel, 28% by weight cobalt, 3% by weight molybdenum, 2.2% by weight titanium and 2% by weight aluminum (balance iron).

The invention described and illustrated is believed to admit of many modifications within the ability of persons skilled in the art, all such modifications being considered within the spirit and scope of the appended claims.

We claim:

1. A method of making a poppet-type valve for an internal-combustion engine which comprises the steps of forming from a relatively high-melting-point material a valve body having a stem and a head extending generally transversely to said stem and providing said valve body with an internal cavity extending from said head into said stem; introducing into said cavity a relatively low-meltingpoint material of high thermal conductivity; sealing said low-melting point material in said cavity; and thereafter etching away any superficial oxide layers present on the surface of said cavity by raising the temperature of said body above the boiling point of said low-melting-point material.

2. A method of making a poppet-type valve for an internal-combustion engine which comprises the steps of forming from a relatively high-melting-point metal a valve body having a stem and a head extending generally transversely to said stem and providing said valve body with an internal cavity extending from said head into said stem; introducing into said cavity a relatively lowmelting-point metal of high thermal conductivity and liquefiable at the operating temperatures of said engine; sealing said low-melting-point metal in said cavity; and thereafter etching away any superficial oxide layers pres ent on the surface of said cavity by raising the temperature of said body above the boilng point of said lowmelting-point metal to about 1000 to 1050 C.

3. A method of making a poppet-type valve for an internal combustion engine which comprises the steps of forming from a relatively high-melting-point metal a valve body having a stem and a head extending generally transversely to said stem and providing said body with at least one internal cavity adapted to extend from said head into said stern upon the welding of said body to hermetically seal said cavity; introducing metallic sodium into said cavity; hermettically sealing said cavity by welding said body closed; and thereafter etching away any superficial oxide layers present on the surface on said cavity by heating said body to a temperature above the boiling point of sodium.

4. The method defined in claim 3 wherein said temperature ranges between substantial-1y 1000 and 1050 C.

5. The method defined in claim 4 wherein said body is formed from a pair of members welded together along a welding seam to hermetically seal said cavity and the heating of said body is maintained for a period sufficient to transform coarse-grain metallic structure in the region of said seam to a fine-grain structure.

6. In a method of making a sodium-filled poppet-type valve for internal-combustion engines the improvement comprising the step of heating said valve to a temperature above the boiling point of sodium to effect an etching by the sodium of surface films of oxides formed between the sodium and the valve body during the production of the sodium-receiving cavity thereof.

7. The method defined in claim 6 wherein said temperature ranges between substantially 1000 and 1050 C.

References Cited UNITED STATES PATENTS 1,984,728 12/1934 Colwell 29156.7 2,273,736 2/1942 Raymond et a1 29407 2,610,279 9/1952 Perkes 29-156.7 2,627,259 2/1953 Wood et al. 29-156.7 3,016,601 1/1962 Tauscher et al. 29-l56.7

JOHN F. CAMPBELL, Primary Examiner.

0 PAUL M. COHEN, Assistant Examiner. 

1. A METHOD OF MAKING A POPPET-TYPE VALVE FOR AN INTERNAL-COMBUSTION ENGINE WHICH COMPRISES THE STEPS OF FORMING FROM A RELATIVELY HIGH-MELTING-POINT MATERIAL A VALVE BODY HAVING A STEM AND A HEAD EXTENDING GENERALLY TRANSVERSELY TO SAID STEM AND PROVIDING SAID VALVE BODY WITH AN INTERNAL CAVITY EXTENDING FROM SAID HEAD INTO SAID STEM; INTRODUCING INTO SAID CAVITY A RELATIVELY LOW-MELTINGPOINT MATERIAL OF HIGH THERMAL CONDUCTIVITY; SEALING SAID 